This application is based upon and claims benefit of priority of Japanese Patent Applications No. 2000-45907 filed on Feb. 23, 2000 and No. 2000-72356 filed or. Mar. 15, 2000, the contents of which are incorporated. herein by reference.
1. Field of the Invention
The present invention relates to an electronic control unit for controlling operation of actuators and to a method of manufacturing the same.
2. Description of Related Art
Electronic control units for use in various controls, such as automotive engine control and transmission control, are generally known. The electronic control unit controls operation of actuators such as electromagnetic solenoids by supplying power thereto based on signals fed to and processed in the electronic control unit. Recent electronic controls for an automotive vehicle are becoming more sophisticated and multi-functional. Electric power to be controlled by driving elements in the electronic control unit is also becoming high. An amount of heat generated in the driving elements such as power transistors or power ICs contained in the electronic control unit becomes high. Such heat is transferred to control elements such as microcomputers contained in the same electronic control unit.
An example of conventional electronic control units is shown in FIG. 1. A circuit substrate 40 on which a driving element 5 and a control element 3 are mounted is contained in a casing 7. A connector 2 for electrically connecting the electronic control unit to outside sensors and actuators is also mounted in the casing. Heat generated in the driving element 5 such as a power transistor is transferred to the control element 3 such as a microcomputer, thereby heating the control element 3. If the control element 3 is excessively heated, its operation stability cannot be maintained. It could be possible to enlarge the circuit substrate 40 to suppress the heat transfer from the driving element 5 to the control element 3. However, it is not preferable, or may not be possible, to enlarge the size of the electronic control unit from viewpoints of a mounting space and a cost of the electronic control unit.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved electronic control unit, in which the heat transfer from the driving elements to the control elements is suppressed without enlarging the size of the electronic control unit.
The electronic control unit according to the present invention. 1 composed of a metal casing, a driving circuit substrate, a control circuit substrate, a flexible printed-circuit sheet connecting both substrates, and a connector for connecting the electronic control unit to outside actuators and sensors. The control circuit substrate includes control elements such as a microcomputer for processing signals fed from the outside sensors and for supplying control signals to the driving circuit substrate. The driving circuit substrate includes driving elements such as power transistors for supplying electric power to the outside actuators based on the control signals fed from the control circuit substrate.
The metal casing has a heat dissipation plate on which the driving circuit substrate generating a large amount of heat is mounted. The control circuit substrate that generates substantially no heat is contained in the casing apart from the driving circuit substrate. A separating space for suppressing heat transfer from the driving circuit substrate to the control circuit substrate is formed between both substrates. The connector is positioned in the separating space. Thus, the separating space in the casing is also utilized as a space for containing the connector. Both substrates are electrically connected by a flexible printed-circuit-sheet which absorbs vibration energy to protect electrical connections. The flexible printed-circuit-sheet is connected to the control circuit substrate at a vicinity of connector pins connecting the connector to the control circuit substrate to reduce electrical resistance in the circuit.
The connector may be mounted on the control circuit substrate and electrically connected thereto. In this case, preferably, both substrates are first connected by the flexible printed-circuit-sheet, and then the connector is mounted on the control circuit substrate to simplify the manufacturing process.
Alternatively, the connector may be mounted on the casing and electrically connected to the flexible printed-circuit-sheet. In this case, preferably, the connector is electrically connected to the flexible printed-circuit-sheet, and then the flexible sheet is electrically connected to both substrates. After that, the connector is mounted on the casing. Elements for absorbing noise coming into the electronic control unit may be surface-mounted on the flexible sheet. Components having inserting leads may also be mounted on the flexible sheet, removing such components from the control circuit board. If no such component is mounted on the control circuit substrate, electrical connections on the control circuit substrate can be carried out only by reflow-soldering. Further, a portion of the flexible sheet on which electric components are mounted may be made of a hard printed-board to secure stable electrical connections against vibration. Components mounted on the flexible sheet may be supported by a holder formed integrally with the connector to secure a higher mechanical strength.
According to the present invention, the driving circuit substrate and the control circuit substrate are positioned in the casing with a separating space therebetween, and the connector is disposed within the separating space. In other words, the separating space for suppressing the heat transfer is also utilized as a space for containing the connector therein. Accordingly, the heat transfer is effectively suppressed without enlarging the size of the electronic control unit.